Iranian-backed militants killed three American service members and more than two dozen others were wounded in an aerial drone attack in Jordan near the Syrian border, President Joe Biden said on Sunday.

Twenty-five troops were injured in the attack by a one-way drone, also known as a "suicide" drone, according to U.S. Central Command, which released a short statement on Sunday confirming the incident.

Biden said in his statement that the U.S. was "still gathering the facts" surrounding the "wholly unjust attack," which he said occurred Saturday night. The White House later clarified that the attack occurred early Sunday in Jordan, or late Saturday Eastern time.

According to an administration official, the attack occurred at the Tower 22 outpost.

The strike marked the first line-of-fire deaths of U.S. troops since the start of the Israel-Hamas war in October, sparked by Hamas' terror attack.

Some of the injured service members received serious wounds from shrapnel and some were being screened for traumatic brain injuries, an official with the White House National Security Council said. The number of injured could change, this official said.

The president on Sunday hailed the killed service members for being "unwavering in their bravery. Unflinching in their duty. Unbending in their commitment to our country."

The U.S. has supported Israel against Hamas in Gaza but sought to prevent the conflict from enveloping the Middle East -- as Iranian-backed militants have carried out a series of strikes in Iraq, Syria and Yemen in opposition to Israel's campaign.

"Have no doubt -- we will hold all those responsible to account at a time and in a manner our choosing," Biden said Sunday.